Given an $x$-monotone curve xcv and an enumeration ce that specifies either the minimum or the maximum end of the curve, determines the location of the curve end along the $x$-dimension.

The variable xcv identifies the parametric curve $C(t) = (X(t),Y(t))$ defined over an open or half-open interval with endpoints $0$ and $1$. The enumeration ce identifies an open end $d \in\{0,1\}$ of $C$. Formally, determines whether $\lim_{t \rightarrow d} X(t)$ evaluates to $b_l$, $b_r$, or a value in between, where $b_l$ and $b_r$ are the $x$-coordinates of the left and right boundaries of the parameter space, respectively. Returns ARR_LEFT_BOUNDARY, ARR_RIGHT_BOUNDARY, or ARR_INTERIOR, accordingly.